pd3463 Wrote:
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> Sorry for the topic derail, but the picture made
> me wonder too, what were the radius limitations on
> these types and how did it compare to the regular
> 4-4-0 and 2-6-0 types of the same time?
>
> Also, I look forward to the answers to the
> original question too.
>
> Phil
I don't know the minimum radius. That being said, the answer is no doubt some variant of, "tighter than is practical." The mason single fairlie type had a reputation for being hard on both track and flanges and didn't particularly like tight curves, and this reputation persisted even after the addition of the lead wheels. In addition, the move to outside valve gear (the early examples had inside stephenson links) created another problem where tight curves would mess with the valve gear setting. The railroad that made the longest use of this style of locomotive (the B,RB&L) was mostly straight with only broad curves.
The front engine wasn't ALL that flexible, much less so than the impression given from photographs. Early examples were, and it was quickly found that on straights the flexibility resulted in rough running and side-to-side hunting. Consequently the design was altered to incorporate significant resistance to lateral motion, which combined with the lead wheels greatly reduced the instability at the cost of also reducing the flexibility that was the design's fundamental purpose. It must be remembered that a conventional locomotive is flexible as well--being jointed between the locomotive and tender, which are all on one frame on the single fairlie. Considering that a short wheelbase Mogul of the time could already manage 25 to 40 degree curves, sometimes tighter, the single fairlie appears to have been intended to solve a problem that wasn't really a problem. In the defense of mason, it must be noted that narrow gauge construction utilizing sharp curves was a new notion in the late 60's and early 70's. When the Transcontinental Railroad was built, 12 to 14 degree curves were regarded as sharp. Moving from that to 20 or 30 degree curves, it's no wonder some designers and engineers might've thought a radical solution was necessary. Further, having acquired the fairlie rights, the MAson Machine Shop no doubt wanted to make good its investment and it's entirely possible that William Mason himself may have liked the aesthetics of the type.
Edited 1 time(s). Last edit at 11/01/2018 10:05AM by James.
